1. Field of the Invention
The present invention relates to a plasma display panel (hereinafter referred to as a xe2x80x9cPDPxe2x80x9d) and a method of forming barrier ribs (partition walls) for the same. More particularly, the invention relates to a method of forming barrier ribs for the PDP that is suitable for a high-definition color display apparatus having a reduced thickness and larger display area. The present invention also relates to a method of forming discharge cells for a plasma display panel. Further, the present invention relates to a phosphor material sheet which is used in the method of forming the discharge cells in the plasma display panel and relates to manufacturing method thereof.
2. Description of the Related Art
A PDP is a display device which serves as flat panel display in large and high-definition color display. The general construction of the PDP includes front and rear glass substrates facing each other with minute spacing and peripherally sealed. Pairs of electrodes are regularly arranged on these two glass substrates, respectively, and a discharge gas mixture containing Ne as a main component is hermetically sealed in the space defined by the two substrates. On the rear glass substrate, a large number of small discharge spaces called discharge cells are formed by line barrier ribs (partition walls). A phosphor is applied to the internal side of each discharge cell. On the opposite front substrate, electrodes facing the discharge cell are provided. By applying a suitable voltage between electrodes, the plasma discharge is induced locally in the discharge gas. ultraviolet ray generated by the plasma discharge induces luminescence of the neighboring phosphors. That is, the discharge cells are used as light emitting elements of the display.
As a method of manufacturing the barrier ribs (partition walls) forming the discharge cells of the PDP, a print laminating method and a sandblasting method are generally known. According to the print laminating method, a the barrier ribs are formed by repeating a step of printing a glass paste onto the rear glass substrate by a screen printing method and drying it until the paste has a height which is required for the barrier rib.
According to the sandblasting method, a thick film made of a barrier rib material (glass paste) is formed on the rear substrate, a subtractive resist. pattern is formed on the thick film by lithography, and the barrier rib material exposed in opening portions of the resist is removed by sandblasting (spraying fine particles mixed into a compressed air at a high speed to physically etch). The resist pattern is removed after the formation of the barrier ribs.
The barrier rib pattern formed by such various methods is fired at a high temperature to form glass barrier ribs. A phosphor material layer (thickness is 20 to 30 xcexcm) is formed in each discharge cell in the next phosphor forming step. The formation of the phosphor material layer employs the screen printing method so far. According to the conventional screen printing method, a phosphor material paste obtained by mixing and kneading a phosphor, an organic binder, a solvent, and the like is supplied to the internal wall of each discharge cell partitioned by the fired barrier ribs.
It is a matter of course that the phosphor material paste of a color corresponding to the color of the pixel of the PDP is supplied to the corresponding discharge cell. Each of R (red), G (green), and B (blue) phosphor material pastes is applied to the inside of-the corresponding discharge cells by the different screen printing step. Namely, there is required to conduct three times printing steps in total in order to supply three different color phosphor material pastes to the corresponding discharge cells.
A technique of photolithography employing photosensitive phosphor material pastes is also examined in place of the screen printing method. According to the method, R/G, and B phosphor material pastes are sequentially applied and procedures such as exposure, development, cleaning, and the like are repeated every phosphor material paste.
The conventional methods of forming the barrier ribs have the following problems. First in the print laminating method, since the thickness of the rib material layer which can be formed in one printing operation is tens of xcexcm at maximum, in order to obtain a height of 100 to 200 xcexcm required for the barrier ribs, it is necessary to repeat printing and drying a large number of times, generally, about ten times. Consequently, there is a problem that the productivity is remarkably low. In an addition, the rib material layer formed by the screen printing has a declined peripheral portion and the raised center portion. When the layers are stacked by printing many times over, the peripheral portions in a sagging form in section are accumulated, so that the bottom of the barrier rib is widened. Consequently, the realization of a high density formation of the barrier ribs is restricted. Further, pitch precision is also limited because of distortion or life of a screen (printing plate), so that it is difficult to realize the large size, high definition, and mass production of the PDP.
As for the sandblasting method, the procedures of formation, elimination, and the like of the resist pattern are complicated. Particularly, when the large-sized display is realized, the scale of an exposing apparatus or a sandblasting apparatus is enormously enlarged, resulting in a sharp increase in cost of equipment. Further, the loss of a material due to sandblast etching is large. Consequently, there is a problem that the manufacturing cost is increased.
Both of the print laminating method and the sandblasting method have the common problem that the shape of the uncured barrier rib is easily deformed due to shrinkage upon firing in a post process. Generally, the shrinkage upon firing can be reduced at a certain degree by raising the content of glass powders contained in the barrier rib material. In this case, however, the flowability of the barrier rib material is contrarily deteriorated. Consequently, it becomes hard to form the fine structures of the barrier ribs, so that there is a problem that formability of the uncured freestanding structures which will be fired to Dorm the barrier ribs, namely, fidelity of the finished barrier ribs is deteriorated.
In order to solve the above-mentioned problems existing in the conventional print laminating method and sandblasting method, it is considered to use a pressure molding method of pressurizing a plane mold onto a thick film made of a barrier rib material formed on a substrate. Also it is considered that a method of photolithography widely used for formation of a-thin film pattern is used for forming the barrier ribs.
The pressure molding method employing the plane mold is excellent because it solves the problems of the printing method and the sandblasting method. Fundamentally, however, the method has a problem that the glass paste is easily partially peeled off from the substrate when the plane mold is separated from the substrate. Therefore, various means for raising adhesive properties of the glass paste to the glass substrate are needed. Selection of the material is restricted and addition of a new process is required. It is difficult to manufacture a large-sized precision mold corresponding to the large size of the substrate, so that a stupendous increase in cost of the apparatus is also conceived as a problem.
The photolithography method employs a photosensitive glass paste and has characteristics such that a precise pattern of barrier ribs can be realized at a high resolution. According to the method, however, processes such as coating/drying of a photo resist, exposure by ultraviolet rays, development, cleaning, and drying are complicated and it takes much time. Surplus materials such as photo resist and developer are required. Expensive apparatuses having a large floor area such as exposing apparatus, developing apparatus, and cleaning apparatus are also needed. Further, the photosensitive glass paste must have larger proportion of resin to glass, as compared with a non-photosensitive glass paste. This causes problems that a degree of shrinkage of the barrier rib structures upon firing is raised, the loss of the material is large, and the like. consequently, it causes an increase in cost.
The conventional method of coating a phosphor material paste has the following problems. As for the method of coating the phosphor material paste by the screen printing method, since the phosphor material paste supplied to the discharge cell is adhered to the rib internal wall by using its material properties, the uniformity of the film thickness of the phosphor is not always guaranteed, so that it is difficult to manage the film thickness. From the viewpoints of life of a screen mask which is used for the screen printing, operating performance, handling such as cleaning, there is a problem that the method is not suitable for mass production of the high-definition large-sized PDP.
In the method of coating the phosphor by the photo-lithography technique, there is required to conduct complicated procedures such as exposure, development, cleaning, and the like. Since two-thirds of the respective color phosphor material pastes applied on the whole surface of the glass substrate is removed by developing process, the efficiency of utilization of the phosphor material paste is deteriorated. In addition, since the removed phosphor material paste is expensive, it is necessary to recover it. Further, the glass substrate has an uneven surface because the barrier rib pattern is formed. Accordingly, it is not easy to remove the phosphor material paste after exposure. Also, the remaining phosphor material paste tends to be contaminated to other color phosphor material pastes. This causes a problem that the mixture of colors easily occurs.
Further, according to the conventional methods, firing for the barrier rib formation and firing after coating the phosphor material pastes, namely, the firing of two times in total is needed. Since the firing process involves heating and cooling, it requires the longest processing time in the whole procedure. Because the firing process must be performed twice, the whole processing time is remarkably extended and the productivity is deteriorated. This also causes an increase in manufacturing cost.
The present invention is accomplished in consideration of the aforementioned circumstances, and a first object thereof is to provide a method of forming barrier ribs of a PDP, wherein barrier ribs for forming discharge cells of the PDP can be formed with high precision, it is suitable for realizing a high-definition and a large size of the PDP, a process is simplified to realize small size and scale of a manufacturing apparatus, occurrence of the loss of a material is prevented, a yield is improved, and a manufacturing cost can be reduced.
A second object of the present invention is to provide method of forming discharge cells of a PDP, wherein barrier ribs partitioning discharge cells in the PDP and a phosphor material layer in the discharge cell can be formed with high precision, it is suitable for realizing a high-definition and a large size of the PDP, a process is simplified to realize small size and scale of a manufacturing apparatus, occurrence of the loss of a material is prevented, a yield is improved, and a manufacturing cost can be reduced.
A third object of the present invention is to provide a sheet made of phosphor materials which is used to form discharge cells for a PDP. Further, it is a fourth object to provide a method of manufacturing the sheet.
According to the present invention, the first object can be attained by a method of forming barrier ribs for a plasma display panel having a plurality of discharge cells intervening between a pair of glass substrates formed with electrodes, the discharge cells being partitioned by the barrier ribs, said method comprising the steps of:
(a) forming an uncured barrier rib material layer having flexibility on the surface of at least one of said glass substrates, on which said electrodes are formed;
(b) rolling a roller, which has an intaglio recessed pattern corresponding to a desired pattern for the barrier ribs on said barrier rib material layer so that the recessed pattern contacts and embosses the barrier rib material layer to form freestanding structures corresponding to the recessed pattern; and
(c) drying and firing a barrier rib material shaped into the freestanding structures, whereby the barrier ribs for partitioning discharge cells are formed on the glass substrate.
In the present invention, the roller having an intaglio recessed pattern corresponding to a desired pattern of the barrier ribs to be formed is used. The intaglio recessed pattern is a recessed and embossed pattern (such as groove pattern) shaped by reversing recessed and embossed portions of the barrier rib structures to be formed. The roller is come into contact with the barrier rib material with pressure while being rotated, so that: freestanding structures of the rib material are formed on the glass substrate by single step operation. The freestanding structures, i.e., uncured barrier ribs (also referred to as xe2x80x9cpre-ribsxe2x80x9d hereinafter) can be converted to barrier ribs by firing.
As a barrier rib material, a material obtained by adding an additive such as alumina, tin oxide, titanium oxide, or zirconium oxide to a glass paste to satisfy required characteristics for barrier rib formation may be used. As for the PDP to which the present barrier ribs forming method can be adopted, there are PDPs of various types such as alternating current surface discharge type, direct current discharge type, and hybrid type. According to the method of the present invention, the intaglio embossed and recessed pattern formed on the roller can form a proper-rib structures such as ribs parallel with stripe-shaped electrodes, ribs. perpendicular to the electrodes, or lattice-shaped (criss-crossing) ribs, which corresponds to the type of the PDP.
It is preferable to apply a release agent to the top surface of the barrier rib material layer in order to improve the release properties to the roller. A talc powder, a powder of a Teflon-based additive, a paste containing the powder, and spray liquid made by dispersing the powder in oil are suitable to the release agent. It is applied thin by a spray or a roll coater. It is preferable that the barrier rib material layer is exposed to or left in the atmosphere of its solvent vapor for a predetermined period of time to be softened, adjusted to have an optimum hardness, and then rolled by the roller. The release agent can be applied after softening in the solvent vapor.
As for the solvent which is used in the softening process, a solvent that is compatible with a resin binder contained in the glass paste may be used. For example, an aromatic solvent such as toluene or higher alcohol may be used. In case of applying the release agent, it is desirable to perform the softening process of the glass paste employing the solvent vapor before coating of the release agent in order to uniformly soften the paste. When the release agent has a nature for allowing the solvent to pass therethrough, the softening process may also be performed after such a release agent is applied.
It is convenient that the barrier rib material layer is formed by laminating a glass paste for rib, which has been previously prepared in a sheet shape, on the glass substrate. Also, the barrier rib material layer can be formed by directly applying a liquid glass paste for rib and drying it. It is desirable to use a white glass paste for rib in this case. The white barrier ribs reflects light emitted in the discharge cells to introduce the-light to the front side of the PDP, so that the efficiency of utilization of light is improved.
Although the barrier ribs are generally formed on the rear glass substrate (back plate) of the PDP, in the case where the ribs are formed on the front glass substrate depending on the type of the PDP, the method of the present invention is applicable to the front glass substrate (front plate) of the PDP. Since the barrier ribs can be formed in various forms such as stripe and lattice, it is a matter of course that the groove pattern on the surface of the roller is made to correspond to the form. For example, when the stripe-shaped ribs should be formed, annular grooves are formed on the roller and, when the lattice-shaped ribs should be formed, lattice-shaped grooves are formed on the roller.
It is necessary to move the peripheral surface of the roller and the glass substrate at the same speed without sliding at a contact portion therebetween. For this purpose, both of them are made to relatively move linearly in such manner that the peripheral velocity of the roller is being allowed to coincide with the relative linear moving speed of the glass substrate to the roller. Although the roller may be relatively moved in one direction only once, it may also be reciprocatingly moved on the same path (passage) plural times. Passing the same path of plural times in this manner enables the grooves to be gradually formed deeply on the rib material layer, so that it is possible to prevent the rib material from adhering to the roller and peeling from the glass substrate.
It is preferable to set the pressing force of the roller to the glass substrate to 20 to 200 kg/cm when the contact width of the roller in the axial direction is set as a reference. The pressing force should be changed depending on conditions such as diameter of the roller, namely, radius of curvature, or hardness of the rib material layer. When the pressing force is smaller than 20 kg/cm, the embossed or protruding portions of the intaglio recessed pattern on the roller cannot be allowed to enter the rib material layer deeply enough, so that it is difficult to obtain enough height of the barrier rib. When it is larger than 200 kg/cm, the shaft of the roller is bent and a difference between the pressing force on a position near the center of the roller in the width direction and one on both the sides increases, so that it is difficult to form reliable barrier ribs with a uniform height or thickness.
The diameter of the roller of 30 to 500 mm is suitable. When the diameter is smaller than 30 mm, the roller is easily bent. When it is larger than 500 mm, the contact area of the roller to the rib material layer is enlarged and the contact portion approximates to the face contact, so that the rib material remains in the grooves of the roller to be easily peeled off from the glass substrate.
It is preferable to set the relative linear moving speed of the glass substrate to the roller to be equivalent to the relative peripheral velocity of the roller to the glass substrate. It is preferably set to 0.02 to 2.0 m/min. When the moving speed is set less than 0.02 m/min, the productivity is remarkably deteriorated. When it is set more than 2.0 m/min, the rib material tends to be easily peeled off from the glass substrate, and therefore, the grooves having sufficient depth cannot be provided on the roller and the rib with sufficient height cannot be formed.
The grooves formed on the roller, namely, annular parallel grooves or lattice-formed (criss-crossing) grooves should be shaped into such a form that it is easily released from the rib material layer. For example, the form in section of the groove perpendicular to the longitudinal direction is shaped into a trapezoid having wide opening or a trapezoid having curved sides. That is, when it is assumed that the opening width of the groove is set to WT, bottom width is set to WS, depth is set to H, and pitch (pitch in the width direction of the groove) is set to LP, it is preferable to form the grooves so as to satisfy the following expressions.
xe2x80x830 less than WB/WT less than 1.0
0.1 less than H/WT less than 3.0
0.1 less than (WT+WB)/2LP less than 1.0
The first object of the present invention can also be attained by a method of forming barrier ribs for a plasma display panel having a plurality of discharge cells. intervening between a pair of glass substrates formed with electrodes, the discharge cells being partitioned by the barrier ribs, said method comprising the steps of:
(a) forming an uncured barrier rib material layer having flexibility on the surface of at least one of said glass substrates, on which said electrodes are formed;
(b) forming on said barrier rib material layer a black mask having a pattern corresponding to a desired pattern of the barrier ribs to be formed;
(c) rolling a roller, which has grooves corresponding to the desired pattern of the barrier ribs, on said barrier rib material layer while maintaining each groove to be positioned between the black masks so that a protruding portion between the grooves contacts and embosses the barrier rib material layer to form freestanding structures having the black mask on the top thereof; and
(d) drying and firing the barrier rib material shaped into the freestanding structure to form the barrier ribs having the black mask on the top thereof.
In this case, the black mask can be simultaneously formed on the top face of each barrier rib in the barrier rib forming step. Consequently, the separate or independent process for the black mask formation is not required. Of course, it is not needed to form the black mask on the front glass plate, separately.
The black mask may be formed on the rib material layer so as to correspond to the stripe-shaped or lattice-shaped rib pattern by a screen printing. In place of the screen printing, a sheet-shaped material comprised of a white rib material and a black rib material superposed thereon at the positions of the ribs can be laminated on the rib material layer.
Further, the first object of the present invention can be attained by a method of forming barrier ribs for a plasma display panel having a plurality of discharge cells intervening between a pair of glass substrates formed with electrodes, the discharged cells being partitioned by the barrier ribs, said method comprising the steps of:
(a) forming an uncured barrier rib material layer having flexibility on the surface of at least one of said glass substrates, on which said electrodes are formed;
(b) uniformly coating the surface of said barrier rib material layer with a photosensitive black rib material;
(c) rolling a roller, which has an intaglio recessed pattern corresponding to a desired pattern for the barrier ribs, on said barrier rib material layer coated with said photosensitive black rib material so that the recessed pattern forms freestanding structures corresponding the barrier ribs on the glass substrate;
(d) partially removing the black rib material so as to leave it on the upper surfaces alone of the freestanding structures by a technique of photolithography; and
(e) drying and firing a barrier rib material with the black rib material shaped into the freestanding structures to form the barrier ribs.
As for the rolling roller which is used for the barrier rib formation, a roller constructed by alternately adhering and fixing two kinds of discs having different outer diameters in the axial direction can be used. In this case, chamfering the outer rim of each disc having a large diameter enables the form of the annular groove in section to be shaped into a trapezoidal form or a trapezoidal form having curved lines. When a large number of notches are formed in each large disc, the lattice-shaped ribs can be formed.
The second object of the present invention is accomplished by a method of forming discharge cells for a plasma display panel having a plurality of discharge cells intervening between a pair of glass substrates formed with electrodes, the discharge cells being partitioned by the barrier ribs, said method comprising the steps of:
(a) forming an uncured barrier rib material layer having flexibility on the surface of at least one of said glass substrates, on which said electrodes are formed;
(b) rolling a rib forming roller, which has an intaglio recessed pattern corresponding-to a desired pattern for the barrier ribs to be formed, on said barrier rib material layer while the peripheral velocity of the rib forming roller is made to coincide with the relative linear moving speed of the glass substrate, so that the recessed pattern embosses the barrier rib material layer to form freestanding structures corresponding to the barrier ribs on the glass substrate;
(c) drying and firing a barrier rib material shaped into the freestanding structures to form the barrier ribs;
(d) laminating a phosphor material sheet, which is formed by uniformly applying a phosphor material to one side of a film base, on the glass substrate so that said phosphor is come into contact with the barrier ribs formed in the step
(e) rolling a phosphor filling roller, which has protruding portions corresponding to the positions of the discharge cells to be formed, on the phosphor material sheet laminated in the step (d) to fill said phosphor into the discharge cells between the adjacent barrier ribs;
(f) peeling the film base from the phosphor material sheet;
(g) removing the excess phosphor which is not supplied to the discharge cells in the step (e) and remained on the top faces of the barrier ribs; and
(h) firing the phosphor filled in the discharge cells.
That is, the phosphor material sheet is laminated on the glass substrate having the barrier ribs thereon and the roller in which the recessed and embossed pattern (groove pattern) obtained by reversing the recessed and embossed surface of the barrier rib structure has been formed on the peripheral surface is rolled on the above laminated sheet, so that the discharge cells between the barrier ribs are filled with the phosphor. As for the phosphor filling roller used in this case, the roller similar to the barrier rib forming roller mentioned above can be used.
In the steps (d) to (g) of supplying the phosphor to the glass substrate on which the barrier ribs are formed, when a PDP capable of color displaying by using different color phosphors is manufactured, the steps of (d) to (g) are repeated for each of the different color phosphor material sheets. They are repeated for each of e.g. R (red), G (green), and B (blue) phosphor material sheets. In place of repeating the steps (d) to (g) for the different colors, repeating the steps (d) to (f) every color and removing all of excess phosphor material pastes in the next step (g) in a lump may also be performed.
The roller (phosphor filling roller) which is used in the step (e) for respective color phosphor material sheets has embossed or protruding portions on the positions of the discharge cells corresponding to respective colors. For the glass substrate having the barrier ribs in, for example, a vertical stripe form thereon, a roller-in which annular embossed lines (protruding portions) are formed at intervals of three pitches of the stripe-shaped discharge cells is used. For the different color phosphor material sheets, the same roller can be used by deviating in the axial direction (width direction) one pitch by one. It is a matter of course that the peripheral velocity of the phosphor filling roller is allowed to coincide with the relative linear moving speed of the glass substrate in a manner similar to the case of the above rib forming roller.
In order to remove the excess phosphor material paste in the step (g), the surface on which the barrier ribs are formed is directed downwardly and a knife edge is moved so as to apply the top face of each barrier rib, so that the excess phosphor adhered on the top face of the barrier rib can be scraped off. Before firing the phosphor material paste, it can be easily scraped off by applying the knife edge. The excess phosphor material paste can be also removed after firing. In this case, it is sufficient to perform scraping off by an abrading apparatus having a rotational abrasive disc made of grindstone and, after that, cleaning.
When the film base of the phosphor material sheet is separated or peeled off in the step (f), the excess phosphor material paste (i.e., phosphor material paste other than the phosphor material paste filled in the target discharge cells) is often adhered to the film base and partly removed from the barrier ribs. In this case, after all of color phosphor material pastes are filled, the excess phosphor material pastes still remaining on the barrier ribs may be removed in a lump.
Preferably, before rolling the phosphor filling roller, the hardness of the phosphor material paste is adjusted by leaving it in a solvent vapor of the phosphor material paste for predetermined period of time. Softening the phosphor material paste and support film enables the pressing force of the phosphor filling roller to be reduced. In this instance, the phosphor material paste has substantially the same composition as that of the glass paste for the barrier rib formation and contains a phosphor material powder in place of the glass powder. As for the film base which is used for the phosphor material sheet, a film having flexibility such that the film is easily extended by the embossed portions of the roller upon rolling the roller, being softened in the solvent vapor or gas and having transmitting properties for the vapor is desirably used.
The phosphor filling roller may be rolled in one direction only once and it can be also relatively moved reciprocatingly on the- same path. It is preferable that the diameter of the phosphor filling roller is set to 30 to 300 mm and the relative peripheral velocity is set to 0.05 to 2.0 m/min.
The second object of the present invention can be accomplished by a method of forming discharge cells for a plasma display panel having a plurality of discharge cells intervening between a pair of glass substrates formed with electrodes, the discharge cells being partitioned by the barrier-ribs, said method comprising the steps of:
(a) forming an uncured barrier rib material layer having flexibility on the surface of at least one of said glass substrates, on which said electrodes are formed;
(b) rolling a rib forming roller, which has the peripheral surface provided with grooves corresponding to the barrier ribs to be formed, on said barrier rib material layer while its peripheral velocity is allowed to coincide with the relative linear moving speed of the glass substrate so that the grooves embosses the barrier rib material layer to form freestanding structures corresponding to the barrier ribs on the glass substrate;
(c) drying and firing a barrier rib material shaped into the freestanding structures in the step (b) to form the carrier ribs partitioning the discharge cells;
(d) superposing a screen mask on the glass substrate and supplying a predetermined color phosphor material paste to the positions of the predetermined discharge cells by a screen printing method;
(e) drying the phosphor material paste supplied in the step (d);
(f) rolling the phosphor filling roller, which has grooves at the same pitches as those of the rib forming roller used in the step (c), on the phosphor material paste so that extruding portions between the grooves contacts and fills the phosphor material paste into the discharge cells;
(g) removing the excess phosphor material paste remained on the top face of each barrier rib; and
(h) firing the phosphor material paste filled in the discharge cells.
The barrier rib forming roller used in the step (b) can be used as a phosphor filling roller used in this case. That is, since the freestanding structures (i.e., uncured barrier ribs, which is also referred to as xe2x80x9cpre-ribsxe2x80x9d) formed by the barrier rib forming roller are shrunk by drying and firing to form the finished barrier ribs in the step (c), gaps are formed between the ribs after firing and the rib forming roller. Therefore, it is possible to fill the phosphor material paste into the discharge cells by using the gaps.
In the case of the PDP for color display, the step (d) is repeated for each of the different color phosphor material pastes. After the color phosphor material pastes are supplied to the corresponding discharge cells, the phosphor material pastes can be filled into all of the discharge cells in a lump in the step (f). When the supply amount of the phosphor material paste to be supplied to the discharge cells by the screen printing in step (d) is set larger than a finally required amount to the discharge cells, a sufficient amount of phosphor material paste can. be filled into each discharge cell but excess phosphor material paste overflows from the discharge cells to the outside. Therefore, the overflowing phosphor material paste may be scraped off by using a knife edge, doctor blade or the like. The excess phosphor material paste can be easily removed before firing the phosphor material paste.
Further, the second object of the present invention is accomplished by a method of forming discharge cells for a plasma display panel having a plurality of discharge cells intervening between a pair of glass substrates on which electrodes are formed, the discharge cells being partitioned by barrier ribs, a phosphor material layer being formed in the internal surface of each discharge cell, comprising the steps of:
(a) forming an uncured barrier rib material layer having flexibility on the surface of at least one of said glass substrates, on which said electrodes are formed;
(b) forming on the barrier rib material layer a phosphor material layer in which phosphor materials are arranged at pitches equivalent to those of the discharge cells to be formed;
(c) rolling a roller, which has an intaglio recessed pattern corresponding to a desired pattern for the barrier ribs to be formed, on said phosphor material layer. and barrier rib material layer so that the recessed pattern forms freestanding structures corresponding to the barrier ribs on the glass substrate and fills the phosphor material in spaces between the adjacent freestanding structures; and
(d) drying and firing a barrier rib material shaped into the freestanding structures and the phosphor material between the freestanding structures, whereby the discharge cells partitioned by the barrier ribs and having the phosphor material layer on the internal surface are formed.
In this aspect of the invention, a lamination of the barrier rib material and phosphor material on the glass plate is simultaneously pressed or rolled by the single roller in which a recessed and embossed pattern (groove pattern) obtained by reversing the recessed and embossed surface of the barrier rib structure is formed on the peripheral surface. A roller similar to the above-mentioned barrier rib forming roller can be used as a rolling roller used in this case.
Preferably, a release agent is applied to or coated on the surface of the barrier rib material layer in order to improve the release properties to the roller. As for the release agent, the talc powder or powder of the Teflon-based additive, paste containing the powder, and spray liquid made by dispersing the powder in oil are suitable. The release agent may be applied thin by the spray or roll coater. It is preferable that the barrier rib material layer be softened by leaving it in its solvent vapor or gas for a predetermined period of time, adjusted to have an optimum. hardness, and then pressurized by the roller. The release agent may also be applied after softening in the solvent vapor.
As for the solvent used in the softening process, a solvent that is compatible with a resin binder contained in the glass paste as a barrier rib material may be used. For example, an aromatic solvent such as toluene or higher alcohol may be used. In case of applying the release agent, it is desirable to perform the softening process of the glass paste by the solvent vapor before coating of the release agent in order to uniformly soften the paste. When the release agent has a nature for allowing a-solvent to pass therethrough, the softening process may be performed after applying the release agent.
It is necessary to move the peripheral surface of the roller and the glass substrate at the same speed without sliding at a contact portion therebetween. For this purpose, both of them are made to relatively linearly move while the peripheral velocity of the roller is allowed to coincide with the relative linear moving speed of the glass substrate to the roller. Although the roller may be relatively moved in one direction only once, it may also be reciprocatingly moved on the same path (passage) plural times. Passing the same path of plural times in this manner enables the grooves to be gradually formed deeply on the rib material layer, so that it is possible to prevent the rib material or phosphor material from adhering to the roller and peeling from the glass substrate.
After the roller is rolled on the phosphor material layer and barrier rib material layer to form the embossed lines corresponding to the barrier ribs [step (c)], a process to form a black mask on the-phosphor material layer at the position of each barrier rib can be added. In this case,-the process for the black mask which is formed on the front glass substrate in the conventional PDP is unneeded or simplified. the black mask can be easily formed by a method such as screen printing.
The phosphor material layer which is formed in the step (b) can be formed on the top surface of the barrier rib material layer by printing. When a black anti-reflection material is contained in the phosphor material layer on positions corresponding to the barrier ribs, the black mask constituted by the black anti-reflection material can be formed together with the barrier ribs and phosphor material layer in the same firing process, so that the productivity is further improved.
When the phosphor material layer is formed by laminating a previously prepared green sheet instead of the printing, the processing efficiency is raised to obtain good working properties. As for the green sheet made of phosphor material which is used in this case, a sheet made by arranging different color phosphor materials so as to correspond to the respective discharge cells is used. The black anti-reflection material can be also contained in the sheet on positions corresponding to the barrier ribs.
The third object of the present invention is accomplished by a sheet made of phosphor materials, which is made by sandwiching different color phosphor materials between a pair of upper and lower detachable film bases so as to correspond to the respective discharge cells. The sheet can be manufactured by the following method.
That is, the fourth object of the present invention can be accomplished by a method of manufacturing a phosphor material sheet which is used to form discharge cells by supplying phosphor to portions between barrier ribs formed on a glass substrate of a plasma display panel, comprising the steps of:
(a) forming a release layer on a lower film base;
(b) printing a first color phosphor to the whole upper surface of said release layer at a uniform thickness;
(c) rolling a first roller on the printed first color phosphor, said first roller having grooves formed on the positions of the discharge cells corresponding to the first color so that said first color phosphor is gathered into the grooves and form first color embossed portions, and drying the formed portions;
(d) printing a second color phosphor to the upper surface of said release layer except said first color embossed portions;
(e) rolling a second roller on the printed second color phosphor, said second roller having grooves formed on the positions of the discharge cells corresponding to the first and second colors so that said second color phosphor is gathered into the grooves of the second roller to form second color embossed portions neighboring the first color embossed portions, and drying the formed portions;
(f) printing a third color phosphor to the upper surface of the release layer except said first and second embossed portions; and
(g) laminating an upper film base through the release layer.